Methods for modifying the surface area of nanomaterials

ABSTRACT

Methods for changing the surface area of nanomaterials to improve properties, processing and product manufacturing. These methods are useful for oxides, nitrides, carbides, borides, metals, alloys, chalcogenides, and other compositions.

RELATED APPLICATIONS

[0001] The present application is a divisional of U.S. patentapplication Ser. No. 10/113,315 filed on Mar. 29, 2003 entitled“POST-PROCESSED NANOSCALE POWDERS AND METHODS FOR SUCH POST-PROCESSING”,which claims the benefit of U.S. Provisional Application No. 60/346,089Filed on Jan. 3, 2002 the specification of which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates, in general, to nanoscale powders,methods for their manufacture, and, more particularly, topost-processing of nanoscale powders.

[0004] 2. Relevant Background

[0005] Powders are used in numerous applications. They are the buildingblocks of electronic, telecommunication, electrical, magnetic,structural, optical, biomedical, chemical, thermal, and consumer goods.On-going market demand for smaller, faster, superior and more portableproducts has demanded miniaturization of numerous devices. This, inturn, has demanded miniaturization of the building blocks, i.e. thepowders. Sub-micron and nanoscale (or nanosize, ultrafine) powders, witha size 10 to 100 times smaller than conventional micron size powders,enable quality improvement and differentiation of productcharacteristics at scales currently unachievable by commerciallyavailable micron-sized powders.

[0006] Nanopowders in particular and sub-micron powders in general are anovel family of materials whose distinguishing feature is that theirdomain size is so small that size confinement effects become asignificant determinant of the materials' performance. Such confinementeffects can, therefore, lead to a wide range of commercially importantproperties. Nanopowders, therefore, are an extraordinary opportunity fordesign, development and commercialization of a wide range of devices andproducts for various applications. Furthermore, since they represent awhole new family of material precursors where conventional coarse-grainphysiochemical mechanisms are not applicable, these materials offerunique combination of properties that can enable novel andmultifunctional components of unmatched performance. Commonly-owned U.S.Pat. No. 6,228,904, which along with the references contained therein ishereby incorporated by reference in full, teach some applications ofsub-micron and nanoscale powders. Co-pending application Ser. No.09/638,977, which is assigned to the assignee of the present inventionand which along with the references contained therein is herebyincorporated by reference in full, teaches exemplary methods forproducing high purity nanoscale materials and their applications.

[0007] In most applications, powders need to satisfy a complexcombination of functional and processing requirements. Submicron powdersin general, and nanoscale powders in particular fail to meet all theserequirements. This invention is directed to address these limitations.

[0008] Nanoscale powders of various compositions can be produced usingdifferent methods. Some illustrative but not exhaustive lists ofmanufacturing methods include precipitation, hydrothermal processing,combustion, arcing, template synthesis, milling, sputtering and thermalplasma. Often, although not always, nanoscale powders produced by suchmanufacturing methods lead to powders that do meet all the requirementsof an end user application. For example, some of the issues limiting thebroad use of nanopowders include,

[0009] 1. Nanoparticles tend to form agglomerates that in some waysbehave like larger particles; there is a need for post-processingtechnologies that can recover the nanoparticles from such agglomerates

[0010] 2. Nanoparticles tend to aggregate thereby making it relativelydifficult to disperse them; there is a need for post-processingtechnologies that can enable ease in the formation of nanoparticulatedispersions in aqueous and non-aqueous solvents

[0011] 3. Nanoparticles offer unusual combination of properties; howeversometimes they are not used because they are not satisfactory in atleast one of the matrix of performance desired for the application;there is a need for post-processing technologies that can enableimprovement in the unsatisfactory performance at an affordable cost

[0012] 4. Nanoparticles tend to adsorb significant levels of gases overtheir high surface areas; alternatively, the surface of nanoparticlesare of a form that makes them incompatible with preferred solvents inspecific applications; there is a need for post-processing technologiesthat can enable improvement in the surface state of nanoparticles toovercome these limitations

[0013] 5. Nanoparticles tend to require very high pressures forcompaction into products. This is in part because of agglomerationand/or high internal friction. Although such high pressures can be usedto consolidate nanoscale powders, this technique is often limited to thepreparation of thin sections due to very high internal residualstresses. Post-processing techniques are needed that can readily formnanostructured products.

[0014] 6. Nanoparticles are difficult to process into components becauseof their unusual rheological and other properties. Post-processingtechniques are needed that can enable reliable, reproducible, andaffordable processing of nanopowders into components.

[0015] Hence, a variety of needs exist for techniques for improvingselected features of sub-micron powders, and specifically nanopowders,to improve the performance of these materials in known applications, andto open up new applications that, until now, were impractical orimpossible.

SUMMARY OF THE INVENTION

[0016] Briefly stated, the present invention involves thepost-processing of nanoscale powders of oxides, carbides, nitrides,borides, chalcogenides, metals, and alloys are described. The powdersare post-processed to improve their functional and processingcharacteristics thereby enabling their widespread use in commercialapplications. Fine powders discussed are of size less than 100 microns,preferably less than 10 micron, more preferably less than 1 micron, andmost preferably less than 100 nanometers. Methods for producing suchpost-processed powders in high volume, low-cost, and reproduciblequality are also outlined.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 shows a schematic block diagram of a process for thecontinuous synthesis of nanoscale powders in accordance with the presentinvention.

[0018]FIG. 2 shows an exemplary overall approach for producing submicronor nanoscale powders in accordance with the present invention.

[0019]FIG. 3 shows an exemplary overall approach for improving thequality of submicron and nanoscale powders produced in accordance withthe present invention; and

[0020]FIG. 4 shows an exemplary overall approach for post-processedpowders into a part or component in accordance with the presentinvention.

[0021]FIG. 5 shows an exemplary process for producing a product ordevice from nanoscale powders produced in accordance with the presentinvention; and

[0022]FIG. 6 illustrates and exemplary with a porosity gradient throughthe thickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention is directed generally at systems andmethods for post-processing of nanoscale powders to alter and improvetheir functional and processing characteristics to more usefully addressthe needs of various applications for the post-processed powders. Inparticular, examples are given of post-processing techniques thataddress agglomeration and aggregation, improve one or more physical,chemical, or solid state properties of the powders, and improve orsimplify the subsequent use of the powders in various applications anddevices. However, the applications of the teachings of the presentinvention are in many cases broader than the specific techniques andsystems taught herein. Accordingly, the basic teachings are readilymodified and adapted to encompass such changes unless specificallytaught otherwise.

[0024] To ease understanding of various techniques and concepts taughtherein, the following definitions are used in the present specification,although the art recognizes various terms not used herein with similardefinitions, and may define specific words and terms used herein withmore general or more specific meanings:

[0025] Definitions

[0026] Fine powders, as the term used herein, are powders thatsimultaneously satisfy the following:

[0027] 1. particles with mean size less than 100 microns, preferablyless than 10 microns, and

[0028] 2. particles with aspect ratio between 1 and 1,000,000.

[0029] Submicron powders, as the term used herein, are fine powders thatsimultaneously satisfy the following:

[0030] 1. particles with mean size less than 1 micron, and

[0031] 2. particles with aspect ratio between 1 and 1,000,000.

[0032] Nanopowders (or nanosize powders or nanoscale powders ornanoparticles), as the term used herein, are fine powders thatsimultaneously satisfy the following:

[0033] 1. particles with mean size less than 250 nanometers, preferablyless than 100 nanometers, and

[0034] 2. particles with aspect ratio between 1 and 1,000,000.

[0035] Pure powders, as the term used herein, are powders that havecomposition purity of at least 99.9%, preferably 99.99% by metal basis.

[0036] Powder, as the term used herein encompasses oxides, carbides,nitrides, chalcogenides, metals, alloys, and combinations thereof. Theterm includes hollow, dense, porous, semi-porous, coated, uncoated,layered, laminated, simple, complex, dendritic, inorganic, organic,elemental, non-elemental, composite, doped, undoped, spherical,non-spherical, surface functionalized, surface non-functionalized,stoichiometric, and non-stoichiometric form or substance.

[0037] To practice the teachings herein, nanoparticles and sub-micronparticles can be produced by any technique. The preferred techniquesincluded herein and identified by reference to other patents and patentapplications are provided as examples to ease understanding andimplementation of the invention.

[0038] A preferred technique for the present invention is to preparenanoscale powders environmentally benign, safe, readily available, highmetal loading, lower cost fluid precursors as shown generally in FIG. 1.The precursor used in operation 101 may be a gas, sol, single-phaseliquid, multiphase liquid, a melt, fluid mixtures and combinationsthereof. Illustration of precursors includes but does not limit to metalacetates, metal carboxylates, metal ethanoates, metal alkoxides, metaloctoates, metal chelates, metallo-organic compounds, metal halides,metal azides, metal nitrates, metal sulfates, metal hydroxides, metalsalts soluble in organics or water, metal containing emulsions. Multiplemetal precursors may be mixed if complex powders are desired.

[0039] Optionally, precursor 101 is purified by any available technique.Whether a precursor 101 benefits from purification is applicationdependent, and dependent on the original purity of the precursor 101.Another optional, application-specific operation is shown by theaddition of synthesis aids in 107. Synthesis aids may be used to affectphysical, chemical, or solid state properties of the powder produced.Synthesis aids 107 may also act as catalysts or buffers in the processof producing powders.

[0040] In the preferred technique, once the desired precursor isavailable, it is processed at high temperatures in 103 to form thepowder 104. Products such as powders 104 produced from these precursorsare pure (i.e., having a high degree of homogeneity of one or moredesired properties such as particle size, particle composition,stoichiometry, particle shape, and the like). It is important that themethod of producing the product and the environment in which theseproducts are produced are pure and compatible with the chemistryinvolved.

[0041] The high temperature processing is conducted at step 103 attemperatures greater than 1000 K, preferably 2000 K, more preferablygreater than 3000 K, and most preferably greater than 4000 K. Suchtemperatures may be achieved by any method such as, but not limited to,plasma processes, combustion, pyrolysis, electrical arcing in anappropriate reactor. The plasma may provide reaction gases or justprovide a clean source of heat. A preferred embodiment is to atomize andspray the feed in a manner that enhances heat transfer efficiency, masstransfer efficiency, momentum transfer efficiency, and reactionefficiency. Method and equipment such as those taught in U.S. Pat. Nos.5,788,738; 5,851,507 and 5,984,997 (and which are herewith incorporatedby reference) are illustrations of various ways the teachings herein canbe practiced.

[0042] In the preferred embodiment, the high temperature processingmethod includes instrumentation that can assist the quality control.Furthermore it is preferred that the process is operated to produce finepowders 104, preferably submicron powders, and most preferablynanopowders. The gaseous products from the process may be monitored forcomposition, temperature and other variables to ensure quality at 105.The gaseous products may be recycled at step 106 or used as a valuableraw material when the powders 108 have been formed as determined at step106 in an integrated manufacturing operation.

[0043] Once the product fine powders 108 have been formed, it ispreferred that they be quenched to lower temperatures to preventagglomeration or grain growth such as, but not limited to, methodstaught in the U.S. Pat. No. 5,788,738. It is preferred that methods beemployed that can prevent deposition of the powders on the conveyingwalls. These methods may include electrostatic, blanketing with gases,higher flow rates, mechanical means, chemical means, electrochemicalmeans, or sonication/vibration of the walls.

[0044] The product fine powders may be collected by any method. Someillustrative approaches without limiting the scope of this invention arebag filtration, electrostatic separation, membrane filtration, cyclones,impact filtration, centrifugation, hydrocyclones, thermophoresis,magnetic separation, and combinations thereof.

[0045]FIG. 2 shows a schematic diagram of a thermal process for thesynthesis of nanoscale powders as applied to precursors such as metalcontaining emulsions, fluid, or water soluble salt. Although a singleprecursor storage tank 204 is shown in FIG. 2, it should be understoodthat multiple precursor tanks 204 may be provided and used with orwithout premixing mechanisms (not shown) to premix multiple precursorsbefore feeding into reactor 201. A feed stream of a precursor materialis atomized in mixing apparatus 203. The precursor storage 204 mayalternatively be implemented by suspending the precursor in a gas,preferably in a continuous operation, using fluidized beds, spoutingbeds, hoppers, or combinations thereof, as best suited to the nature ofthe precursor. The resulting suspension is advantageously preheated in aheat exchanger (not shown) preferably with the exhaust heat and then isfed into thermal reactor 201 where the atomized precursors are partiallyor, preferably, completely transformed into vapor form.

[0046] The source of thermal energy in the preferred embodiments is acombination of heat of reaction in series with a plasma generator 202powered by power supply 206. Plasma gas 207, which may be inert orreactive, is supplied to plasma generator 202 along with any otherdesired process gas 208. Alternatively, the source of thermal energy maybe internal energy, heat of reaction, conductive, convective, radiative,inductive, microwave, electromagnetic, direct or pulsed electric arc,nuclear, or combinations thereof, so long as sufficient to cause therapid vaporization of the powder suspension being processed.

[0047] In preferred embodiment, the atomized feed first combusts to forma hot vapor and it is this hot vapor that interacts with the plasma; inthis embodiment, the feed is not directly injected into the plasma.Optionally, in order to prevent contamination of the vapor stream causedby partial sublimation or vaporization, the walls of reactor 201 may bepre-coated with the same material being processed.

[0048] The vapor next enters an extended reaction zone 211 of thethermal reactor that provides additional residence time, as needed tocomplete the processing of the feed material and to provide additionalreaction and forming time for the vapor (if necessary). As the streamleaves the reactor, it passes through a zone 209 where the thermokineticconditions favor the nucleation of solid powders from the vaporizedprecursor. These conditions are determined by calculating thesupersaturation ratio and critical cluster size required to initiatenucleation. Rapid quenching and highly concentrated feeds lead to highsupersaturation which gives rise to homogeneous nucleation. The zones201, 211, and 209 may be combined and integrated in any manner toenhance material, energy, momentum, and/or reaction efficiency.

[0049] As soon as the vapor has begun nucleation to form nanoscaleclusters, the process stream is quenched in an apparatus withinnucleation zone 209 to prevent the products from growing or sintering orreaching equilibrium. The quench apparatus may comprise, for example, aconverging-diverging nozzle-driven adiabatic expansion chamber at ratesat least exceeding 1,000 K/sec, preferably greater than 1,000,000 K/sec,or as high as possible. A cooling medium (not shown) may be utilized forthe converging-diverging nozzle to prevent contamination of the productand damage to the expansion chamber. Furthermore, near-sonic velocitiesor supersonic velocities may be employed to prevent collisions betweenthe nanoscale particles. Rapid quenching with high velocities ensuresthat the powder produced is homogeneous in composition, its size isuniform, it is free flowing and the mean powder size remains insubmicron scale.

[0050] The quenched gas stream is filtered in appropriate separationequipment in harvesting region 213 to remove the submicron powderproduct 308 from the gas stream. As well understood in the art, thefiltration can be accomplished by single stage or multistage impingementfilters, electrostatic filters, screen filters, fabric filters,cyclones, scrubbers, magnetic filters, or combinations thereof. Thefiltered nanopowder product is then harvested from the filter either inbatch mode or continuously and then transported using screw conveyors orgas-phase solid transport or other methods known in the art. The powderproduct stream is conveyed to post-processing unit operations discussedbelow.

[0051] The purpose of post-processing is to enhance the performance orprocessability of a nanopowder, which may be produced by any syntheticprocess, into a product at an affordable cost. Some of thesepost-processing techniques are discussed below. These post-processingsteps may be done alone or in combination in any order. Quality controltechniques and distributed instrumentation network may be employed atany stage to enhance the performance of nanoscale powders manufactured.

[0052]FIG. 3 depicts exemplary equipment that can be used forpost-processing. The powders to be post-processed are delivered into apost processing equipment 301. One or more instrument ports such as 302interfaces a powder quality measurement system to the chamber 301 and toone or more instruments 303. The instruments 303 implement methods tomeasure powder quality, a computer, and a software to control the postprocessing step. Some non-limiting illustration of instruments 303include X-ray diffractometer, surface area instrument, laser or lightscattering, photo-correlation spectroscopy, angle of repose measurementinstrument, imaging instrument, zeta potential instrument, acousticanalysis instrument, and others. The instrument 303 monitors the qualityof the powders as post-processing progresses and evolves or stops thepost-processing profile in accordance with software settings. Thistechnique can ensure the quality and consistency of the powdersproduced.

[0053] In a preferred embodiment, the instrument 303 comprises a systemcapable of producing an electromagnetic feed signal. This feed signalinteracts with the nanoscale particles being processed in chamber 301.The feed signal after interacting with the particles creates one or moreproduct signals because of scattering, reflection, diffraction,emission, refraction, transmission, absorption, impedance, or acombination of these effects. One or more of these product signals arethen received by receiving part of instrument 303. A resident softwareinstalled on a computing platform then interprets the product signal,mathematically transforms it into a numeric quantity if appropriate,compares the numeric quantity with calibrated responses resident in theinstrument, and determines the particle quality at specific time andspace. To illustrate, but not limit, the product signal transformationstep can utilize Scherrer analysis of peak broadening detected in adiffraction pattern of electromagnetic waves at specific wavelengths. Insome cases, just the peak broadening (or product signal generated) at aspecific wavelength may be a sufficient and convenient way for real-timequality control. In other cases, a reference sample may be employed andthe signal from chamber 301 may be compared against the reference sampleto determine the deviation from the reference sample. When particles aredispersed in a fluid media, lasers may be the preferred electromagneticfeed signal. In yet other cases, sound or ultrasonic waves may beemployed instead of or with electromagnetic waves to establish thepowder quality. Finally, it should be noted that such in-situ qualitycontrol techniques could be employed during nanoscale powder synthesisor post-processing (e.g., in process 106 shown in FIG. 1).

[0054]FIG. 4 illustrates in flow diagram form a generalized process forproducing post-processed powders that encompasses the various specificexamples provided herein. The operations shown in FIG. 4 are preferablyperformed in a continuous manufacturing process, however, it iscontemplated that powder production may be performed as a separateprocess from the post-processing operations.

[0055] Operations 401 and 402 describe generally operations relating tothe initial manufacture of nanoscale powders, such as by the morespecific operations described in reference to FIG. 1. At 405, thenanoscale powders are characterized to identify performance limitations.Operation 405 typically involves identifying characteristics that areundesirable in a particular application. For example, some applicationsmay tolerate agglomeration, but nevertheless benefit from altering thephase or surface composition of the powder. Characterization 405 focuseson specific characteristics desired by an application.

[0056] In operation 407, and appropriate post-processing regimen isselected based upon the characterization 405 and the desiredcharacteristics of an application. In each specific example below,post-processing operation 407 is performed to affect the powder in aparticular way. Multiple post-processing operations 407 may be performedto alter multiple characteristics. After powders have been postprocessed, operation 409, which is similar to operation 405,characterizes the powder attributes to determine whether characteristicssatisfy desired application characteristics. If not, additional postprocessing can be performed by returning to operation 407. Otherwise thepost-processed powder, can be used in the desired application at 409.

[0057] 1. Modify the Degree of Agglomeration:

[0058] Nanopowders tend to form agglomerates. These agglomerates tend toadversely affect further processing of nanopowders into usefulnanostructured components. One aspect of the invention involvestechnologies that can prevent and/or address the problem of agglomerateformation. As discussed above, appropriate synthesis can impact theformation of free-flowing nanoscale powders, particle collisions at hightemperatures, and degree of agglomeration. In case nanoscale powdershave undesirable degree of agglomeration, this can be addressed bypost-processing in many cases.

[0059] Agglomerates may be of several types. Soft agglomerates are thosewhere the neighboring particles forming the agglomerate are weaklyattached. Hard agglomerates are those where the neighboring particlesforming the agglomerate are sintered to some extent with their neighborsat their grain boundaries; such sintering leads to strong chemical bondsbetween the particles.

[0060] Soft agglomerates can be broken down into independent particlesby providing shear forces, or other type of stress, such as those in aball mill, or jet mill, or other types of mill, or sonication, orimpaction of particles on some surface. Other methods that can provideshear or stress can be utilized. It is important that the temperature ofthe particles during de-agglomeration be kept below a temperature wheresintering begins. It is suggested that the post-processing of softagglomerates be preferably done at temperatures below 0.5 times themelting point of the substance in Kelvin, more preferably below 0.35times the melting point, and most preferably below 0.25 times themelting point. If necessary, external cooling or cryogenic cooling maybe employed.

[0061] In another embodiment, the milling environment is grounded asnanoparticles tend to develop static charge. In yet another preferredembodiment, the milling environment is provided with a fluids such asbut not limiting to organic acid vapors or liquids, alcohols, aldehydes,ketones, aromatics, monomers, amines, and imines. Such an environmentpacifies the surfaces and prevents reformation of soft agglomerates oncethe milling stops.

[0062] Hard agglomerates can be post-processed by techniques disclosedfor soft agglomerates above. However, the energy required for separatingsintered particles is often significant. Therefore, a preferred methodis to provide a reactive media that can assist separation of the hardagglomerates into independent particles. In a preferred embodiment, asolvent that dissolves the substance being processed is used as thereactive media. Preferably, the reactive media tends to dissolve thesintered interfaces (necks) preferentially and thereby acceleratesstress-induced separation of the particles. The reactive media should beselected such that it does not dissolve the particulates completely. Itshould be noted that such post-processing will lead to dissolution ofthe substance into the media which in turn will change the state of themedia. It is therefore preferred that the post-processing medium bemonitored and refreshed thereby maintaining the preferred environment.To illustrate but not limit, alumina nanoparticles are known to dissolvein highly alkaline solutions. Thus, hard agglomerates comprising aluminananoparticles can be post-processed in a mill and an alkaline medium.The alkaline media is expected to assist the milling process. However,as alumina dissolves, it is expected that the pH of the medium willchange. It is preferred that the media be refreshed, by replacement orrecycle or addition, to a pH that provides desired post-processingperformance.

[0063] During the post-processing of hard agglomerates, in anotherpreferred embodiment, the milling environment is provided withappropriate and compatible surface adhering fluids such as but notlimiting to organic acids, alcohols, aldehydes, ketones, aromatics,dispersants, monomers, amines, and imines. Such an environment pacifiesthe surfaces and prevents formation of agglomerates once the millingstops.

[0064] In summary, according to this aspect of the invention, thegeneric method for post-processing agglomerated submicron or nanoscalepowders comprises: (a) synthesizing the powders; (b) determining thenature of agglomerates; (c) transferring the said agglomerated powdersinto an equipment; (d) applying shear or other stress to theagglomerated powders, commensurate with the determined nature ofagglomerate, while maintaining the average temperature less than 0.5times the melting point of the powder in Kelvin for a period sufficientto break the agglomerated powder into de-agglomerated powder; (e)collecting the de-agglomerated powder. This method can further compriseadding a reactive media or a surface adhering fluids or both before theshear step.

[0065] 2. Modify the Surface:

[0066] One of the features of nanoparticles is their high surface area.This surface often is covered with functional groups or adsorbed gasesor both. This can cause difficulty in processing the powders into afinished product. In some applications, it is necessary that the surfacebe modified to simplify product manufacturing and to improve theconsistency and reliability of the finished product.

[0067] Commonly owned U.S. Pat. No. 6,228,904, incorporated herein byreference, teaches several methods for modifying the surface ofsub-micron and nanoscale powders. Surface modification can beaccomplished in a number of ways. The surface modification may includeone or more of the following steps: (a) the water content on the powdersurface is brought to a desired value followed by a wash of the surfacewith hydrolyzing species (such as but not limiting to organometallics,alkoxides) thereby functionalizing the surface of the powders; (b) thepowder is heated in vacuum to remove adsorbed species; thereafter thepowder is treated to species of choice to cover its surface area; (c)the powder is first washed with an organic acid (such as but notlimiting to oxalic acid, picric acid, acetic acid) which is thenfollowed by a treatment with surface stabilizing species such as but notlimited to nitrogen containing organic compounds, oxygen containingorganic compounds, oxygen and nitrogen containing organic compounds,chalcogenides containing organic compounds, polyalkylimines,polyalkeneimines, and quartemary ammonium species; (d) the powdersurface is reduced or oxidized selectively to form a thin, preferably amonolayer, of functionalized surface. In these methods, the volumefraction of the species or substance that is functionalizing the surfaceis preferably given by:

γ_(s)<1/(d _(p) /3+1)

[0068] Where, γ_(s) is the volume fraction of the species that isfunctionalizing the nanomaterial surface and d_(p) is the average domainsize of the nanomaterial in nanometers. While the above equation is thepreferred guideline, higher volume fractions may be utilized for certainapplications. The motivation for these and other surface modificationpost-processing steps is to produce an interface that makes thenanoscale powders easier to process or easier to include as aconstituent in the final product while retaining the benefits ofnanoscale dimensions in the final product.

[0069] As a particular example, nanoscale silica particles can besurface treated with organosilicon compounds. For example,hexamethyldisilazane is used to make silica surface hydrophobic. Thehydrophobicity results from the treatment with hexamethyldisilazane,which replaces many of the surface hydroxyl groups on the silicananoparticles with trimethylsilyl groups. One aspect of the presentinvention involves the selection of the composition of the specieschosen to treat the surface of a nanopowder in a manner that enhancesthe performance of the treated powder. While the prior art methods canbe utilized for the purposes and motivations outlined in thisspecification, it is preferred that the composition of the species thatis functionalizing the nanomaterial surface be chosen to enhance theperformance of the treated powder. In majority of cases, a non-siliconcomposition is anticipated to be preferred for surface treatment.

[0070] 3. Modify the Near-Surface Composition:

[0071] As mentioned above, one of the features of nanoparticles is theirhigh interface area. The performance of a nanostructured productprepared from nanoscale powders is therefore strongly affected by theperformance of the interface. Some non-limiting illustrations ofinterface influence on the performance of a nanostructured productincludes the high interface diffusivity, electrochemical properties,phonon pinning, catalytic properties, optical properties, andsize-confined electrical and thermoelectronic properties. Apost-processing step that can modify the interface composition cansignificantly impact the performance of the product that comprises suchnanoscale powders.

[0072] One method for modifying the near-surface composition is topartially reduce the composition. For example, an oxide nanopowders iftreated with hydrogen or ammonia or carbon monoxide or methanol vaporsat moderate temperatures for a pre-determined time can lead to a powdercomposition where surface of the nanopowder is deficient in oxygen whilethe bulk retains full stoichiometry. Similarly, if the nanoscale powderis treated with methane in the presence of carbon, the surface of thenanopowder can be transformed into an oxycarbide or carbide, while thecore of the particle remains an oxide. Alternatively, carbothermicnitriding conditions can be used to produce nitride rich surfacecomposition. It is important that carbothermic nitriding be done in thepresence of a stoichiometrically excess of carbon to prevent excessivecoarsening and sintering of the particles. Boron rich surfacecompositions can be achieved by carbothermic reduction in presence ofborane or other boron containing compounds. It should be noted thatthere is no need to completely change the composition of the nanoscalepowder. The benefits of improved performance can be achieved by forminga nanoscale powder with a composition gradient, i.e., where the surfaceis of one desired composition (stoichiometric or non-stoichiometric),the core of the particle is of another desired composition(stoichiometric or non-stoichiometric), and the particle's compositiontransitions from the core to that at the surface.

[0073] Yet another embodiment of the current invention is to usemechanically fused coatings on submicron or nanoscale powders to changethe surface composition. This approach essentially involves high shearmixing where the shear energy is high enough to fuse one composition onthe surface of the other. This approach can significantly impact theflowability, angle of repose, shape, physical and chemical property ofthe composite particle. Furthermore, this approach can produce powderswith characteristics that are not achievable by either of the powdersalone or by a simple non-fused blend of the powders.

[0074] Yet another embodiment of the current invention is to coat thesubmicron or nanoscale powders with another material followed by heattreating the particle to induce chemical reaction(s) that change thesurface composition. This process, for illustration, can comprise (a)coating submicron or nanoscale particles with an organic or inorganic ormetallorganic substance, (b) placing the particles in an equipment wherethe said powders can be heated in an environment of desired pressure,temperature, and gas composition, (c) heating the particles through alinear or non-linear temperature profile, (d) holding the particles atdesired temperatures for a suitable length of time, (e) cooling theparticles to room temperature, and (f) removing the particles from theequipment and using it in a suitable application. These steps canfurther comprise steps where suitable instruments are employed tomonitor and control the feed, or process, or products, or a combinationof these. It is expected that such heat treated of coated particles canmodify the near-surface composition of the particles and therefore theirperformance.

[0075] 4. Modify the Phase:

[0076] Post-processing can be used to modify the phase of nanoparticles.The phase of the particle affects its performance and suchpost-processing can therefore be useful. For example, thermal treatment(cryogenic or high temperature) of an oxide can be used to change anorthorhombic or triclinic or monoclinic phase to cubic phase.Alternatively, anatase phase can be changed to rutile phase or reverse.Pressure can be combined with thermal treatment to achieve phase change.

[0077] Another embodiment of this invention is to use electrical currentto modify the phase of the material. While not exclusively limited toconducting materials, electrical transformation can be particularlysuitable in conducting materials (oxides, non-stoichiometric materials,non-oxides) since electrical current can also provide nominal levels ofohmic heating. Similarly magnetic field can be used to modify the phaseof a material.

[0078] 5. Modify the Surface Area of the Particles

[0079] One of the motivating factors for using nanoparticles is theirunique surface area. Often, the surface area of the powder is dependenton the processing method and processing conditions used to produce thepowders. Techniques that can enhance the surface area of a low surfacearea powder can make the powder more desirable in certain applications.This is often difficult to do.

[0080] In one embodiment aiming to engineer the particle surface area,the particles are produced with another sacrificial compound thatretains its identity. The sacrificial compound is then removed byextraction or dissolution into a suitable medium. For example, zincoxide can be co-synthesized with zirconium oxide followed by dissolutionof zinc oxide in a medium of suitable pH. The zinc oxide can be recycledto reduce the cost of the nanoparticle manufacture. This process, inmore generic sense, can be described as a method for increasing thesurface of submicron or nanoscale particles comprising (a) mixing theprecursor for submicron or nanoscale particles desired with a precursorof sacrificial composition, (b) synthesizing and collecting theparticles as a composite of the desired particle composition and thesacrificial composition, (c) extracting the sacrificial compositionusing a suitable solvent from the composite particle to achieve thedesired surface area, (d) if desired, washing the particles to removetraces of solvent, and (e) if desired, further post-processing theparticles to meet customer requirements. Some illustrations of suchsacrificial compositions include zinc oxide, magnesium oxide, calciumoxide, alkaline metal oxides, tin oxide, antimony oxide, indium oxide,multi-metal oxides, chalcogenides, halides, and water soluble salts.

[0081] In another embodiment, the particles of desired composition areproduced with another sacrificial metal or alloy that retains itsidentity in the composite particle. The sacrificial metal or alloy isthen selectively removed by extraction or dissolution into a suitablemedium as explained above. Some illustrations of such sacrificialcompositions include transition metals, semi-metals, and various alloys.

[0082] In some cases, it is possible that the particles of desiredcomposition may by themselves be soluble in a solvent. In these cases,the surface area of the particles can be modified by direct dissolutionin a suitable solvent for appropriate period of time. In yet anotherembodiment, the submicron or nanoscale particles may be milled in asolvent to modify the surface area or other characteristics of theparticles. It all cases, it is preferred that the solvent used fordissolution process is replenished to maintain the best dissolutionkinetics. The replenishment can be achieved by removing, recovering andrecycling the solvent. It is also preferred that the dissolution processconditions such as temperature and mixing rates are engineered andinstrumented for high productivity.

[0083] In another embodiment, instead of using a sacrificial compositionthat can be removed using a solvent, a sacrificial composition that canbe removed by sublimation may be preferred. For this embodiment,compounds or metals or alloys with high vapor pressures at moderatetemperatures, such as less than 975K, are preferred. In this embodiment,vacuum may be employed to reduce the time needed to sublime thesacrificial composition.

[0084] 6. Modify the Shape

[0085] One of the desirable features in particle technology is theability to control particle shape. Quite often, the shape of very smallparticles is spherical. However, a number of applications preferparticles with an aspect ratio greater than 1.5, more preferably greaterthan 3.0, and even more preferably greater than 10.0. Techniques thatcan modify the shape of a particle can also enhance the surface area ofa powder.

[0086] One post-processing technique for modifying shape is catalytictransformation. This process, in more generic sense, can be described asa method for modifying the shape of submicron or nanoscale particlescomprising (a) mixing the submicron or nanoscale particles or theirprecursors with a catalyst that preferentially favors dissolution andprecipitation of the particles, (b) processing the mixture at atemperature greater than 300K, preferably greater than 1000K (c)collecting the particles with desired aspect ratio, and (d) if desired,further post-processing the particles to meet customer requirements. Inthis embodiment, the catalytic reactions are preferably conducted in agas phase.

[0087] Another post-processing technique for modifying shape is the useof shear at temperatures where the material softens. As a rule of thumb,this temperature for many composition is between 0.2*T_(m) and0.95*T_(m), where T_(m) is the melting point of the composition inKelvin.

[0088] Yet another post-processing technique for modifying shape is tomix the particles in a polymer followed by thermal treatment of the mix.The thermal treatment is anticipated to cause sintering and growth ofthe particle into particle shapes of desired aspect ratio. Techniquessuch as extrusion may be employed before the thermal treatment tocontrol the aspect ratio of the particles.

[0089] Still another post-processing technique for modifying shape is todeposit the submicron or nanoscale particles in a template followed bythermal treatment between 0.2*T_(m) and 0.95T_(m), where T_(m) is themelting point of the composition in Kelvin. Illustrative templatesinclude anodized aluminum, anodized silicon, other anodized metals,micro-machined templates, porous polymers, radiation templated polymers,zeolites, emulsion produced templates, and other templates. The templatecan be removed using solvents and other techniques after the desiredaspect ratio particles have been produced.

[0090] 7. Post-Processing of Nanopowders to Achieve Consolidation

[0091] Once the nanoscale powders have been post-processed, they may betransformed into a useful product. For example, coatings, casting,molding, compacting, spraying, pressing, electrodeposition, and othertechniques followed by thermal treatment for consolidation and sinteringare exemplary techniques for manufacturing or forming useful productsfrom post-processed powders in accordance with the present invention.

[0092] One illustrative method is carefully controlled slurryprocessing. Briefly, the slurry process entails the dispersion ofpowders in a liquid medium that contains a solvent, as well as organicconstituents added to tailor the rheological properties of thedispersion and the mechanical properties of the product after thesolvent is removed by drying. The solvent can be aqueous or non-aqueous;many slip systems are formulated with organic solvents includingalcohols, ketones, and hydrocarbons. Dispersants are an importantadditive since they prevent agglomeration and coagulation of the powdersin suspension. Dispersion can be facilitated by steric repulsion,meaning adsorbed molecules physically interfere with those of otherparticles, or electrostatic repulsion, which employs the repulsivenature of particles with a similar surface charge. Commonly employedchemical dispersants are carboxylic acids and phosphate esters forsolvent-based systems. In practice, most systems are stabilized by acombination of electrostatic and steric mechanisms.

[0093] Dispersing nanopowder slurries is not a trivial process.Agglomeration in slip systems causes problems similar to those thatoccur as a result of agglomeration in dry pressing. In this case,however, the agglomerates can be broken by the application of aggressiveforces during processing. Exemplary methods that can be utilized areball milling, high power ultrasonic agitation, or shear homogenization.Applying these processes to powder suspensions can lead to a green body(i.e., unfired) with a very high density (i.e., >65%); this body, inturn can be sintered to near theoretical density.

[0094]FIG. 5 illustrates this aspect of the disclosed inventionschematically. The details of the invention are as follows:

[0095] A. Nanocrystalline ceramic powder produced in 501 and isformulated into a slurry, slip or ink in 503. An illustration ofpreferred embodiment, but in no way limiting the scope of thisinvention, is as follows: 10 vol. % nanocrystalline SiC powder, acationic dispersant in the level 2 mg/m², a polymeric binder, andtoluene are ball-milled with zirconia media in a polyethylene bottle for12 hours.

[0096] B. The slip is tape-cast in 505 into a layer, preferably 0.1 to1000 microns thick, more preferably that is 1 to 100 microns thick, andmost preferably that is 5-50 microns thick.

[0097] C. Multiple sheets or layers produced in 505 are stacked to yieldthe desired thickness, and the layers are laminated together.

[0098] D. The laminated layers are sectioned in 507 to yield theappropriate component geometry. In operations 509 and 511, thesectionals can be stacked in a desired order, and pressed and cured toform a working structure.

[0099] E. The component is placed in a furnace and sintered in operation513, when appropriate, to full density (e.g., 1400° C. for zirconia).Operation 513 yields a device, part or component that can then beprocessed through various finishing operations 515 such as polishing,terminating, electroding, passivating, packaging, or otherdevice-specific processes.

[0100] Distinctive features of this invention relate to the quality ofthe final product and the low-cost and flexibility of the processing.Using multiple tape cast layers allows layers to be formed in a widevariety of shapes and sizes using inexpensive and efficient equipment.Active layers (i.e., layers comprising materials designed to perform aspecific device function) can be intermixed with non-active layers thatprovide structural support, electrical or mechanical connectivity, andother supporting functions. Stacking tape cast layers into laminatestructures allows control over device shape in three-dimensions. Adifferentiating factor of the proposed invention, over prior art, is thebenefit of a nanocrystalline structure in the finished product.

[0101] The advantages of nanomaterials such as increased hardness andwear-resistance, novel electrical properties, electrochemicalproperties, chemical, thermal, magnetic, thermoelectric, sensing,optical, electro-optical, display, energetic, catalytic, and biologicalproperties will benefit many engineering applications.

[0102] Possible compositions of the active layer include but are notlimited to organic, inorganic, metallic, alloy, ceramic, conductingpolymer, non-conducting polymer, ion conducting, non-metallic,ceramic-ceramic composite, ceramic-polymer composite, ceramic-metalcomposite, metal-polymer composite, polymer-polymer composite,metal-metal composite, processed materials including paper and fibers,and natural materials such as mica, dielectrics, ferrites,stoichiometric, non-stoichiometric, or a combination of one or more ofthese. Illustrative compositions include but are not limited to doped orundoped, stoichiometric or non-stoichiometric titanium oxide, bariumtitanate, strontium titanate, zinc oxide, zinc sulfide, indium oxide,zirconium oxide, tin oxide, antimony oxide, tungsten oxide, molybdenumoxide, tantalum oxide, cerium oxide, rare earth oxides, silicon carbide,hafnium carbide, bismuth telluride, gallium nitride, silicon, germanium,iron oxide, titanium boride, zirconium boride, zirconates, aluminates,tungstates, carbides, manganates, ruthenates, borates, hydrides, oxides,oxynitrides, oxycarbides, halides, silicates, phosphides, nitrides,chalcogenides, complex oxides such as dielectrics and ferrites.

[0103] Additionally, the active layer can be porous or dense, flat ortapered, uniform or non-uniform, planar or wavy, straight or curved,non-patterned or patterned, micron or sub-micron, grain sized confinedor not, or a combination of one or more of these.

[0104] The solvent for the slip can be organic, inorganic, emulsion,aqueous, acidic, basic, neutral, charged, uncharged, stable ormetastable. The stacking can be manual, automatic, computer aided,optically aligned, or robotically aligned.

[0105] In one embodiment, the slip, slurry, or ink can comprisenanoscale powders only along with the solvent. In another embodiment,the slip, slurry, or ink can comprise can be a mixture of nanoscalepowders, submicron, and micron sized powders. In yet another embodiment,the slip, slurry, or ink can comprise nanoscale powders as dopants. Themix may be heterogeneous or homogeneous, the latter being preferred. Forthe scope of this invention, the slip, slurry, or ink has greater than0.01% of its total solids as added nanoscale size powders.

[0106] The tapes can be stacked in any pattern. The device may just haveone layer or multiple layers, the preferred embodiment being multiplelayers. The individual layers can be the same or different formulation.Additionally, it is possible to replace or combine one of the activelayers with a layer capable of a secondary but desired function. Forexample, one or more of the layers can be replaced with resistive layersby design to provide heat to the device or component. In some situationsit may be desirable to have one or more active layers replaced with EMI(electromagnetic interference) filter layers to minimize noise byinductively or capacitively coupling with the active layer. In anothersituation, one of the layers can be air or an insulating layer in orderto provide thermal isolation to the active layer. In yet anothersituation, sensing layers may be provided sense the temperature ordensity or concentration of one or more species in the feed or processedor recycle stream. In yet another situation, electrochemical couplelayers may be provided to internally generated electricity and energyneeded to satisfactorily operate the device. In other conditions, theelectrode layers can be provided to function as anodes and cathodes. Insome situations, the device may be a minor part of the multilaminatedevice and the device containing device can have primary function ofreliably providing an electrical, thermal, magnetic, electromagnetic,optical, or structural function in an application. The layers can alsocomprise multilaminates of different material formulations. Thesedifferent formulations can have different properties that allow thefabrication of a functionally graded material (FGM).

[0107] The multilayer stack may have a rectangular shape. However, thestack shape can also be circular, elliptical or any other shape.Additionally, the edges may be rounded or sharp. The product could befinished, polished, cut, plated, terminated, rounded, radiativelytreated, or processed further with the motivation to improve propertiesor to impart new performances.

[0108] 8. Uses

[0109] Applications provided by this invention include: surgical blades,cryogenic slicing, blades for cutting polymers and fabrics, blades forscissors, utility knives, hunting knives, snap knives, and art & hobbyknives. Ceramic blades are currently being proposed in theaforementioned applications due to the fact that they outwear steelknives 50-100 times and carbide knives 7 to 10 times. The cost driversfor blades used in industrial applications is quite high due to the factthat the downtime associated with replacing a blade is more costly(i.e., non-productive downtime) than the material for the blade. Thisinvention proposes to leapfrog the current technology by reducing costs,and by extending the performance of the part and the lifetime of theblades significantly. Any structural components could be manufacturedusing this invention with the motivation to reduce cost, increasevolume, and/or improve performance. Additional applications includeceramic, metal, or composite seals. These low-profile components can befabricated by a multi-layer build-up process described in FIG. 5.

[0110] An additional application of the teachings herein is functionallygraded parts or components that are dense or porous. Illustrationincludes a filter with a porosity gradient through the thickness asshown in FIG. 6, for example. In the filter application shown in FIG. 6,a relatively thick porous substrate 601, an intermediate porosity layer602, and a nanocrystalline layer 603 having low relative porositycomprise similar materials, and may use a single powder composition as astarting material. Post-processing techniques described herein are usedto alter the porosity of the powder as it is deposited or formed on thepreceding layers using, for example, the slurry processing techniquesdescribed above.

[0111] This invention is contemplated to have application in thebiomedical field, among other fields. For example, the present inventionmay be applied to producing implant materials, monitors, sensors, drugdelivery devices, and biocatalysts from nanoscale powders using themulti-layer laminating process to produce three-dimensional shapes.

[0112] This invention may also be applied the solid oxide fuel cell(SOFC) area. Zirconia is one of the materials that has been investigatedas the solid electrolyte for SOFC's. Solid electrolyte components can bemade by tape casting multi-layer devices with a very high surface area(i.e., nanomaterial based electrolytes).

[0113] Additionally, the post-processed nanopowders made in accordancewith the present invention may be used to produce electrical devicessuch as varistors, inductors, capacitors, batteries, EMI filters,interconnects, resistors, thermistors, and arrays of these devices fromnanoscale powders. Moreover, magnetic components such as giantmagnetoresistive GMR devices may be manufactured from nanoscale powdersproduced in accordance wit the present invention as well as in themanufacture thermoelectric, gradient index optics, and optoelectroniccomponents from nanoscale powders.

[0114] The teachings in this invention are contemplated to be useful inpreparing any commercial product from nanoscale powders whereperformance is important or that is expensive to produce or is desiredin large volumes. Moreover, post-processed fine powders have numerousapplications in industries such as, but not limiting to biomedical,pharmaceuticals, sensor, electronic, telecom, optics, electrical,photonic, thermal, piezo, magnetic, catalytic and electrochemicalproducts. Table 1 presents a few exemplary applications ofpost-processed powders. TABLE 1 Post-processed Ceramic NanopowderApplication Composition Capacitors, Barium titanate, strontium titanate,barium strontium Resistors, Inductors, titanates, silicates, yttria,zirconates, nanodopants, Integrated Passive fluxes, electrodeformulations Components Substrates, Alumina, aluminum nitride, siliconcarbide, Packaging cordierite, boron carbide, composites PiezoelectricPZT, barium titanate, lithium titanates, nanodopants transducers MagnetsFerrites, high temperature superconductors Electroptics (Pb, La)(Zr,Ti)O₃, nanodopants Insulators Alumina Varistors ZnO, titania, titanates,nanodopants Thermistors Barium titanates, mangnates, nanodopants FuelCells Zirconia, ceria, stabilized zirconia, interconnects materials,electrodes, bismuth oxide, nanodopants Mechanical Silicon nitride,zirconia, titanium carbide, titanium components, nitride, titaniumcarbonitride, boron carbide, boron sealants, adhesives, nitride,dispersion strengthened alloys gaskets, sporting goods, structuralcomponents Biomedical Aluminum silicates, alumina, hydroxyapatite,zirconia, zinc oxide, copper oxide, titania Coatings Indium tin oxide,nanostructured non-stoichiometric oxides, titania, titanates, silicates,chalcogenides, zirconates, tungsten oxide, doped oxides, concentriccoated oxides, copper oxide, magnesium zirconates, chromates,oxynitrides, nitrides, carbides, cobalt doped titania PigmentsOxynitrides, titania, zinc oxide, zirconium silicate, zirconia, dopedoxides, transition metal oxides, rare earth oxides Engineered plasticsSilicates, zirconates, manganates, aluminates, borates, barytes,nitrides, carbides, borides, multimetal oxides Catalysts Aluminumsilicates, alumina, mixed metal oxides, zirconia, metal doped oxides,zeolites Abrasives, Aluminum silicates, zirconium silicates, alumina,Polishing Media ceria, zirconia, copper oxide, tin oxide, zinc oxide,multimetal oxides, silicon carbide, boron carbide

[0115] Other embodiments of the invention will be apparent to thoseskilled in the art from a consideration of the specification or practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with the true scope andspirit of the invention being indicated by the claims.

9. EXAMPLE 1

[0116] The following batch was mixed: AMOUNT MATERIAL DESCRIPTION (Vol.%) SiC NRC powder 10 A 203 Dispersant 3.3 B74001 (solids) Binder 10.4B74001 (liquid) Binder 8.5 Toluene Solvent 77.8

[0117] The mixture was milled with zirconia media for 12 hours in apolyethylene bottle. After milling, the slip was removed from the bottleand tape cast (Model #101, Drei-Tech Corporation) through a 165 microngap doctor blade. The final thickness of the tape after drying wasapproximately 30 microns. A total of 33 layers of tape were stacked andtacked (Model #NT300, Pacific Trinetics Corp., San Marcos, Calif.) underSiC blades. The layers were then laminated together at a temperature ofapproximately 65° C. at a pressure of 26.7 MPa in an isostaticlamination system (Model #IL-4004, Pacific Trinetics Corp., San Marcos,Calif.). The binders were burned out in nitrogen (Model #Inert Gas Oven,Blue M Electric, Watertown, Wis.) with the following schedule: 2° C./minto 200° C. for 1 hour, and 1° C./min to 550° C. for 6 hours.

[0118] The laminated material was sectioned with a commerciallyavailable razor blade into the approximate geometry of the finishedblade. An edge was put into the SiC blade by sandwiching it between twopieces of stainless steel and holding it at an angle of 45 degrees (seeFIG. 1) while running it across SiC abrasive paper (1200 grit).

10. EXAMPLE 2:

[0119] The following batch was mixed: AMOUNT MATERIAL DESCRIPTION (Vol.%) SiC Superior Graphite 059 10 A 203 Dispersant 1.1 B74001 (solids)Binder 12.2 B74001 (liquid) Binder 20.9 Toluene Solvent 55.8

[0120] The balance of the process was conducted in accordance withExample 1.

11. EXAMPLE 3 Thermistor

[0121] Nanoscale barium titanate slip is prepared. An ink of nickel isprepared. A tape of barium titanate is formed. The tape is sliced intosections and electrode applied on one surface. Alternating stacks oftitanate and nickel electrode are placed to form a multilayer structure.The laminate is cured and then diced into multilayer PTC thermistorelements. The elements are sintered into dense structure and thenterminated. The resulting device is used to control and monitortemperature. Alternatively, they are used as electromagnetic energylimiting devices. In another example, the titanate powder can bereplaced with nanoscale manganate powder to form an NTC multilayerthermistor.

[0122] Although the invention has been described and illustrated with acertain degree of particularity, it is understood that the presentdisclosure has been made only by way of example, and that numerouschanges in the combination and arrangement of parts can be resorted toby those skilled in the art without departing from the spirit and scopeof the invention, as hereinafter claimed.

We claim:
 1. A method for modifying the surface area of a composition ofmatter comprising: preparing nanomaterials composite comprising asacrificial composition and a desired composition wherein thesacrificial composition retains its identity; treating the nanomaterialscomposite by processing the nanomaterials composite with a solvent;wherein the treatment step modifies the surface area of thenanomaterials composite by removing the sacrificial composition; andcollecting treated nanomaterials comprising the desired composition. 2.The method of claim 1 further comprising a step wherein the treatednanomaterials composite is washed to remove traces of the solvent. 3.The method of claim 1 wherein the desired composition comprise asubstance selected from the group consisting of: oxides, carbides,nitrides, chalcogenides, metals, and alloys.
 4. The method of claim 1wherein the sacrificial composition comprises a substance selected fromthe group consisting of: zinc oxide, magnesium oxide, calcium oxide,alkaline metal oxides, tin oxide, antimony oxide, indium oxide, andmulti-metal oxides.
 5. The method of claim 1 wherein the sacrificialcomposition comprises a substance selected from the group consisting of:chalcogenides and water soluble salts.
 6. The method of claim 1 whereinthe sacrificial composition comprises a substance selected from thegroup consisting of: metal, semi-metal and alloy.
 7. The method of claim1 wherein the pH of the solvent is adjusted to assist the removal of thesacrificial composition.
 8. The method of claim 1 wherein the removal ofthe sacrificial composition occurs because of dissolution of thesacrificial composition.
 9. The method of claim 1 wherein the solvent isreplenished during the treatment step.
 10. The method of claim 1 whereinthe treated nanomaterials comprise a purity greater than 99.9% by metalbasis.
 11. The method of claim 1 wherein the nanomaterials comprise anaspect ratio greater than
 1. 12. A method for modifying the surface areaof a composition of matter comprising: preparing nanomaterials compositecomprising a sacrificial composition and a desired composition whereinthe sacrificial composition retains its identity; treating thenanomaterials composite by processing the nanomaterials composite undera condition that causes removal of the sacrificial composition andmodification of the surface area of the nanomaterials composite; andcollecting the treated nanomaterials composite comprising of the desiredcomposition.
 13. The method of claim 12 wherein the condition thatcauses removal of the sacrificial composition comprise vacuum.
 14. Themethod of claim 12 wherein the condition that causes removal of thesacrificial composition comprise a temperature less than 975 K.
 15. Themethod of claim 12 wherein the desired composition comprise a substanceselected from the group consisting of: oxides, carbides, nitrides,chalcogenides, metals, and alloys.
 16. The method of claim 12 whereinthe treated nanomaterials comprise a purity greater than 99.9% by metalbasis.
 17. The method of claim 12 wherein the nanomaterials comprise anaspect ratio greater than 1.